This invention relates to a polymer electrolyte which is excellent in oxidation resistance, of a low cost and has a high durability suitable for electrolyte membranes used for fuel cells, electrolyitic apparatuses of water, hydrohalogenic acids and sodium chloride, oxygen enrichers, humidity sensors, gas sensors, etc., and for other like uses, and to a polymer electrolyte membrane, a polymer electrolyte membrane/electrode assembly and a fuel cell which use the polymer electrolyte.
Fluorine-containing electrolytes typically represented by perfluorohydrocarbonsulfonic acid membranes have a very high chemical stability because they have C—F bonds. Therefore, said fluorine-containing electrolytes are in use for the above-mentioned solid polymer electrolyte membranes for fuel cells and electrolytic apparatuses of water, sodium chloride and hydrohalogenic acids and, by virtue of their protonic conductivity, for humidity sensors, gas sensors, oxygen enrichers, and the like.
Said fluorine-containing electrolytes, however, are very expensive because they are produced by a special process. Furthermore, halogen compounds require sufficient consideration in the aspect of equipment to cope with environmental pollution in synthesis and discarding. Accordingly, a polymer electrolyte of a non-fluorine-containing protonic conductor which is inexpensive and environmentary-friendly is eagerly awaited.
As to inexpensive solid polymer electrolyte membranes, there have been disclosed sulfonated aromatic hydrocarbon type electrolyte membranes including sulfonated polyether ether ketone in JP-A-6-93114, sulfonated polyether sulfone in JP-A-9-245818 and JP-A-11-116679, sulfonated acrylonitrile-butadiene-styrene copolymer in JP-A-10-503788, sulfonated polysulfide in J.P. Appl. Kohyo-11-510198 and sulfonated polyphenylene in J.P. Appl. Kohyo-11-515040.
The above-mentioned sulfonated aromatic hydrocarbon type electrolyte membranes, as compared for example with fluorine-containing electrolyte membranes represented by Nafion, are easy to produce and of low cost, but are more susceptible to oxidative degradation and desulfonation.